Prevention strategies have been developed to take advantage of the metabolic and behavioral risk factors for type 2 (non-insulin-dependent) diabetes which have been identified in research with the Pima Indians and elsewhere. Obesity, impaired glucose tolerance, hyperinsulinemia, physical inactivity, and high fat diet have been implicated as risk factors for type 2 diabetes. Since these factors are potentially reversible with behavioral and pharmacologic therapy, strategies for prevention have been developed and will be tested. This project is a multicenter randomized clinical trial of prevention of type 2 diabetes in overweight persons with impaired glucose tolerance known as the Diabetes Prevention Program. During the project year, the initial treatment phase was completed ahead of schedule because of the strong beneficial effects of the interventions. The incidence rate of diabetes was reduced by 31% by metformin and 58% by a lifestyle modification program. Long-term followup of participants continues.